Freshwater aquaculture comprises land based production with runoff to freshwater, as well as cage production in freshwater. The request is restricted to rainbow trout, brown trout and Arctic char for fish production but is in some areas also relevant to hatchery production.

Monitoring of water quality

Physical conditions such as water quantity, water depths, receiver capacity for pollution, currents and renewal of water, is more limited in lakes than in the sea.

- The consequence is that fresh water farms must be smaller. Signs of pollution from fish farms will appear at an earlier stage than in the sea, and monitoring of water quality in and outside the farm is important to ensure good conditions for the fish, says Ulf Erikson, who participated in the risk assessment work in the VKM Panel for animal health and animal welfare.

Need more knowledge about the recommended fish density

Data for recommended fish density is limited, especially related to trout farming. This applies in particular to assess the total fish welfare by density limits.

Nevertheless, it seems appropriate to tentatively recommend fish densities of less than up to 80 kg/m3 in case of rainbow trout, whereas for Arctic char higher densities can be recommended, possibly within the range of 75-150 kg/m3. Relevant fish density data for brown trout is basically lacking.

Risk for infectious diseases

If only local stocks are used, the risk is low. Use of other sources of roe and fish will increase the risk. Use of Norwegian or imported, disinfected roe is associated with low to moderate risk, depending on the source. The risk with use of Norwegian or imported fish is considered to be moderate to high. The same risk profile applies for the use of slaughter pens. If the pens are established to keep fish originating from another water system, new diseases may be introduced and the health risk will increase.

- Well trained farmers and fish health professionals will increase the likelihood of rapid detection and possibilities to take prompt action. Mandatory harvesting, fallowing and disinfection will reduce the chance of an undetected disease to establish itself, says Erikson.

Commissioned by NFSA

NFSA has asked VKM to assess the risk of infection and the risk of poor welfare in freshwater aquaculture. The reason for the request is that the Ministry of Fisheries and Coastal Affairs has asked NFSA to review the fish health and welfare regulations designed to reduce the regulatory burden and improve the opportunities for freshwater aquaculture.

VKM’s Panel on Animal Health and Animal Welfare has been responsible for the risk assessment. The project consisted of three experts from the research group and two national external experts. The project was led by Dr. Ulf Erikson.